Conventionally, a flow rate measuring device has a construction in which a detection element is placed in a flow channel and an air flow rate is measured. However, if the flow rate measuring device is used for a long term, dust in air adheres to and accumulates on the detection element, and measurement accuracy deteriorates. This may become a cause of failure.
In order to eliminate such a defect, there is a dust trap device having a structure in which trap walls are provided in a flow channel, dust in an airflow is caught by the trap walls so as to be separated by means of utilizing an inertial force of dust that goes straight, and only a clean airflow is led to the detection element (for example, see Patent Document 1).    Patent Document 1: JP11-166720A